geranyl diphosphate is first stereospecifically isomerized to linalyl diphosphate which, following rotation about C-2-B-3 to the cisoid conformer, cyclizes from the anti-endo configuration. Neryl diphosphate cyclizes either directly or via the linalyl intermediate without the attendant rotation

Requires Mg2+. The enzyme from Salvia officinalis (sage) can also use (3R)-linalyl diphosphate or more slowly neryl diphosphate in vitro [3]. The reaction proceeds via isomeration of geranyl diphosphate to (3R)-linalyl diphosphate. The oxygen and phosphorus originally linked to C-1 of geranyl diphosphate end up linked to C-2 of (+)-bornyl diphosphate [3]. cf. EC 5.5.1.22 [(-)-bornyl diphosphate synthase].

bornyl diphosphate synthase is responsible for the first step in camphor biosynthesis producing bornyl diphosphate, which is subsequently hydrolyzed to borneol and then oxidized to camphor, pathway overview

the C-terminal domain catalyzes the cyclization of geranyl diphosphate, orienting and stabilizing multiple reactive carbocation intermediates. The N-terminal domain has no clearly defined function, although its N-terminus caps the active site in the C-terminal domain during catalysis

the reaction mechanism in BPPS involves the following steps: binding of geranyl diphospahte, metal-activated ionization to yield an allylic transoid carbocation, formation of (3R)-linalyl diphosphate, rotation around the C2-C3 bond and ionization to generate a cisoid allylic cation in the reactive conformation, cyclization to form a (4R)-R-terpinyl cation, further cyclization to yield (+)-2-bornyl cation, and reincorporation of the diphosphate by the (+)-2-bornyl carbocation, to yield the final product (+)-bornyl diphosphate in ca. 75% yield

(di)terpene synthases seem to mediate specific reaction outcomes, at least in part, by providing electrostatic effects to counteract those exerted by the diphosphate co-product. Role for the diphosphate anion co-product in the reaction catalyzed by monoterpene cyclases, such as bornyl diphosphate synthase, hydroxyl dipole stabilization of the specific carbocation formed by initial cyclization, enabling deprotonation of this early intermediate, whereas the lack of such stabilization, i.e. in the presence of an aliphatic side chain leads to carbocation migration towards the pyrophosphate co-product, resulting in a more complex reaction. The 7-aza-7,8-dihydrolimonene analogue is clearly bound backwards to enable aza-diphosphate ion-pairing, indicating that this is the thermodynamically favored binding mode for such a carbocation. The diphosphate co-product is tightly bound and may serve as a general acid/base during terpene synthase reactions without becoming reattached itself. Consistent with such tight binding is the stereospecificity of bornyl diphosphate formation by BPS, which reattaches the bornyl cation to the same oxygen of the diphosphate involved in the original diphosphate ester bond of the GPP substrate, indicating that the diphosphate anion remains in a fixed orientation during the catalyzed reaction

(di)terpene synthases seem to mediate specific reaction outcomes, at least in part, by providing electrostatic effects to counteract those exerted by the diphosphate co-product. Role for the diphosphate anion co-product in the reaction catalyzed by monoterpene cyclases, such as bornyl diphosphate synthase

competitive inhibition, the aza-analog of the substrate is bound anomalously, perhaps as a consequence of the positive charge, bond distortion, or hydrogen bonding resulting from the N for C substitution, binding strutcure, overview

competitive inhibition, the enantioselective synthase readily distinguishes between (3R)- and (3S)-homolinalyl diphosphates, both of which were more effective inhibitors than is 3-azageranyl diphosphate, the fluorinated analogues prove to be the most potent competitive inhibitors

hanging-drop vapor-diffusion method, structure of complexes with aza analogues of substrate and carbocation intermediates, as well as complexes with diphosphate and bornyl diphosphate, determined at 2.0 A resolution